Process for the preparation of hydrogen and carbon monoxide

ABSTRACT

A catalytic partial oxidation process for the preparation of hydrogen and carbon monoxide from an organic feedstock, which process comprises contacting the organic feedstock and an oxygen-containing gas, in amounts giving an oxygen-to-carbon ratio of from 0.3 to 0.8, with a catalyst at a gas hourly space velocity in the range of from 100,000 to 10,000,000 Nl/kg/h, in which process the organic feedstock used is a feedstock containing hydrocarbons and/or oxygenates, which feedstock is liquid under conditions of standard temperature and pressure and has an average carbon number of at least 6.

The invention relates to a process for the preparation of hydrogen andcarbon monoxide by the catalytic partial oxidation of appropriatefeedstocks.

The partial oxidation of gaseous hydrocarbons, in particular methane ornatural gas, in the presence of a catalyst is an attractive route forthe preparation of mixtures of carbon monoxide and hydrogen, normallyreferred to as synthesis gas. The partial oxidation of gaseous methaneis an exothermic reaction represented by the equation:

2CH₄+O₂→2CO+4H₂

There is literature in abundance on the catalysts and the processconditions for the catalytic partial oxidation of, in particular,methane. Reference is made, for instance, to EP-A-303 438, EP-B-262 947,U.S. Pat. No. 5,149,464, International patent application publicationNo. WO 92/11199 and to publications by D A Hickman and L D Schmidt(“Synthesis Gas Formation by Direct Oxidation of Methane over PtMonoliths”, J of Catal. 138, 267-282, 1992), A T Ashcroft et al.(Selective oxidation of methane to synthesis gas using transition metalcatalysts”, Nature, vol. 344, No. 6264, pages 319-321, 22^(nd) March,1990), P D F Vernon et al (“Partial Oxidation of Methane to SynthesisGas”, Catalysis Letters 6 (1990) 181-186), R H Jones et al. (“CatalyticConversion of Methane to Synthesis Gas over Europium Iridate, EU₂Ir₂O₇”,Catalysis Letters 8 (1991) 169-174) and J K Hockmuth (“Catalic PartialOxidation of Methane over a Monolith Supported Catalyst”, AppliedCatalysis B: Environmental, 1 (1992) 89-100), and EP-A-656 317.

In EP-A-656 317 the catalytic partial oxidation of methane at high gashourly space velocities, i.e. in the range of from 20,000 to 100,000,000h⁻¹, is mentioned.

It will be clear that because of the H/C atomic ratio of methane (4), itis the best feedstock when large amounts of hydrogen are to be produced.When considering other sources for producing hydrogen it will be clearthat hydrocarbons having more than 1 carbon atom have a lower H/C ratiowhich makes them less ideal.

Moreover, there is a well-known tendency of hyrocarbons having more than1 carbon atom to be susceptible to the pyrolitic production of carbonrather than producing optimal amounts of H₂ and CO. This tendencybecomes more pronounced as the number of carbon atoms in the hydrocarbonmolecule increases. Apart from this tendency to form pyrolytic carbon,higher hydrocarbons also suffer from the intrinsic properties thatmixtures of such hydrocarbons with air are very unstable and may lead topre-emission ignition which is highly undesired.

Further, it is well-known that carbon deposits may also be caused bycatalytic reactions and, again, this tendency will be more pronouncedsubjecting higher hydrocarbons to catalytic processes.

The catalytic partial oxidation of hydrocarbons which are liquid underconditions of standard temperature and pressure to hydrogen and carbonmonoxide has been disclosed in U.S. Pat. No. 4,087,259. Liquid hourlyspace velocities (LHSV), i.e. litres hydrocarbon per litre catalyst perhour, of from 2 to 20 h⁻¹ are exemplified, which is equal to a gashourly space velocity of up to 75,000 h⁻¹ for a mixture of air andgasoline. It is explicitly mentioned that a LHSV greater than 25 h⁻¹will result in incomplete partial oxidation and thus in a lower yield.

In EP-A-262 947 the catalytic partial oxidation of hydrocarbons having 1to 15 carbon atoms is disclosed. For methane, GHSV's of up to 42,500 h⁻¹are described. It is mentioned in EP-A-262 947 that for higherhydrocarbons a lower GHSV will be chosen than for hydrocarbons having alower number of carbons. For hexane, very low throughputs, i.e. 6.25 and12.5 g/h, are exemplified. These throughputs correspond, with GHSV'sbelow 1,000 Nl/kg/h. For a oxygen-to-carbon ratio in the range of from0.3 to 0.8, the hexane conversion is, even at these low throughputs,below 80%.

The aim of the present invention is to provide a process for thepreparation of hydrogen and carbon monoxide from organic feedstocks thatare liquid under conditions of standard temperature and pressure (25° C.and 1 atm) at a very high yield, while avoiding the accumulation ofcarbon deposits on the catalysts.

Surprisingly, it has now been found that these requirements can befulfilled by performing a catalytic partial oxidation process withorganic feedstocks that are liquid under conditions of standardtemperature and pressure at an oxygen-to-carbon ratio in the range offrom 0.3 to 0.8 and at very high gas hourly space velocities.

Accordingly, the present invention relates to a catalytic partialoxidation process for the preparation of hydrogen and carbon monoxidefrom an organic feedstock, which process comprises contacting theorganic feedstock and an oxygen-containing gas, in amounts giving anoxygen-to-carbon ratio of from 0.3 to 0.8, with a catalyst at a gashourly space velocity in the range of from 100,000 to 10,000,000Nl/kg/h, in which process the organic feedstock used is a feedstockcontaining hydrocarbons and/or oxygenates, which feedstock is liquidunder conditions of standard temperature and pressure and has an averagecarbon number of at least 6.

The average carbon number can be calculated by a summation of the carbonnumber times the mole fraction for all fractions. Thus, the averagecarbon number n is defined as:

n=Σn _(i) .x _(i)

wherein n_(i) is the carbon number of a fraction i and x_(i) is the molefraction of fraction i.

In particular, the feedstocks to be used in the process according to thepresent invention contain hydrocarbons or mixtures of hydrocarbonsboiling in the range of from 50° C. to 500° C., preferably in the rangebetween 60° C. and 350° C. Suitable feedstocks comprise kerosenefeedstocks boiling between 150° C. and 200° C., synthetic gasoilfeedstocks boiling between 200° C. and 500° C., in particular between200° C. and 300° C. The hydrocarbons to be used may be derived frombiomass, such as for example biodiesel.

In order to measure the suitability of the feedstocks to be used in theprocess according to the invention, it may be useful to refer to thesmoke point of the feedstock envisaged since the smoke point of thefeedstock is an indication of the propensity of the feedstock towardsthe generation of carbonaceous deposits.

In general, smoke points (as determined by ASTM-D 1322-96) of more than15 are representative of the feedstock for the catalytic partialoxidation. Preferred feedstocks have a smoke point of at least 18, morepreferred above 25 whilst feedstocks having a smoke point of more than60 such as synthetic gasolines (e.g. as produced via the Shell MiddleDistillate Synthesis process can be suitably applied).

Another indication of the propensity of the feedstock towards thegeneration of carbonaceous deposits is the content of sulphur and metalssuch as Ni or V in the feedstock. Suitably, the sulphur content of thefeedstock used in the process of the invention is below 150 ppm,preferably below 100 ppm. The content of Ni or V is suitably below 0.2ppm, preferably below 0.1 ppm.

It is possible to have hydrocarbonaceous material present in thefeedstocks to be used in the process according to the present inventionwhich are gaseous under standard conditions of temperature and pressureprovided the requirements of the feedstock being liquid under standardconditions of temperature and pressure and having an average carbonnumber of at least 6 are still met.

Hydrocarbons which are liquid under standard conditions of temperatureand pressure contain up to 25 carbon atoms in their molecules.

The process according to the present invention can also be carried outwhen the feedstock contains oxygenates being liquid under standardcondition of temperature and pressure and having an average carbonnumber of at least 6.

Oxygenates to be used as (part of) the feedstock in the processaccording to the present invention are defined as molecules containingapart from carbon and hydrogen atoms at least 1 oxygen atom which islinked to either one or two carbon atoms or to a carbon atom and ahydrogen atom.

Examples of suitable oxygenates are alkanols, ether, acids and estershaving between 6 and 25 carbon atoms and being liquid under standardconditions of temperature and pressure.

Also mixtures of hydrocarbons and oxygenates as defined hereinbefore canbe used as feedstock in the process according to the present invention.Both hydrocarbon feedstocks and oxygenate-feedstocks (and theirmixtures) may contain oxygenates having less than 6 carbon atoms such asmethanol, ethanol, dimethyl ether and the like, provided therequirements of the feedstocks being liquid under standard conditions oftemperature and pressure and the average carbon number of the feedstockbeing at least 6 are met.

The feedstock to be used in the process according to the presentinvention is contacted with an oxygen-containing gas during the partialoxidation process.

Air may be used as the oxygen-containing gas, in which case nitrogenwill be present in the feed and reaction mixture in large quantities.Alternatively, substantially pure oxygen or oxygen-enriched air may beused.

The feed may optionally comprise steam.

The feed normally comprises the hydrocarbon and/or oxygenate feedstockand oxygen in an amount sufficient to give a oxygen-to-carbon ratio inthe range of from 0.3 to 0.8, preferably from 0.45 to 0.75.Oxygen-to-carbon ratios of the stoichiometric ratio, 0.5, that is in therange of from 0.45 to 0.65 are particularly preferred. References to theoxygen-to-carbon ratio refer to the ratio of oxygen in the form ofmolecules (O₂) to carbon atoms present in the hydrocarbon and/oroxygenate feedstock.

If steam is present in the feed, the steam-to-carbon ratio (that is theratio of molecules of steam (H₂O) to carbon atoms in the hydrocarbon) ispreferably in the range of from above 0.0 to 3.0, more preferably fromabove 0.0 to 2.0.

The process according to the present invention may be operated at anysuitable pressure. Preferably, the catalytic partial oxidation processis operated at elevated pressures, that is pressures significantly aboveatmospheric pressure. The process may be operated suitably at pressuresin the range of from 2 to 50 bar. Preferably, the operating pressure isin the range of from 3 to 30 bar, more preferably in the range of from 5to 20 bar. References in this specification to ‘bar’ are to ‘barabsolute’.

The catalytic partial oxidation process may be operated at any suitabletemperature. Under the preferred conditions of high pressure prevailingin the catalytic partial oxidation process, the feed molecules aretypically allowed to contact the catalyst at elevated temperatures inorder to achieve the level of conversion required for a commercial scaleoperation. Accordingly, the process is preferably operated at atemperature of at least 800° C. Preferably, the operating temperature isin the range of from 800 to 1500° C., more preferably in the range offrom 800 to 1350° C. Temperatures in the range of from 850 to 1300° C.are particularly suitable. Reference herein to temperature is to thetemperature in the top (i.e. the upstream side) layer of the catalyst.

The oxygen-containing gas is provided during the catalytic partialoxidation process at gas space velocities (expressed as normal litres(i.e. litres at 0° C. and 1 atm.) of gas per kilogramme of catalyst perhour) which are in the range of from 100,000 to 10,000,000 Nl/kg/hr,preferably in the range of from 200,000 to 3,000,000 Nl/kg/hr, morepreferably in the range of from 400,000 to 3,000,000 Nl/kg/hr. Spacevelocities in the range of from 500,000 to 1,500,000 Nl/kg/hr areparticularly suitable.

Catalyst compositions suitable for use in the catalytic partialoxidation of gaseous hydrocarbons as known in the art can also beapplied in the catalytic partial oxidation of hydrocarbons and/oroxygenates in accordance with the present invention. Such catalystsgenerally comprise, as active component, a metal selected from GroupVIII of the Periodic Table of the Elements. References in thisspecification to the Periodic Table of the Elements are to the CASversion, as published in the CRC Handbook of Chemistry and Physics, 68th Edition. Catalysts for use in the process of the present inventioncomprise, as the catalytically active component, a metal selected fromrhodium, iridium, palladium and platinum.

Catalysts comprising rhodium, iridium or platinum are particularlysuitable catalysts. Iridium containing catalysts are most preferred.

The catalytically active metal is most suitably supported on a carrier.Suitable carrier materials are well known in the art and include therefractory oxides, such as silica, alumina, titania, zirconia andmixtures thereof. Mixed refractory oxides, that is refractory oxidescomprising at least two cations may also be employed as carriermaterials for the catalyst. Also metals, preferably in the form ofgauzes, can be suitably applied as carrier material.

The catalytically active metal may be deposited on the carrier bytechniques well known in the art. A most suitable technique fordepositing the metal on the refractory carrier is impregnation, whichtechnique typically comprises contacting the carrier material with asolution of a compound of the catalytically active metal, followed bydrying and calcining the resulting material. For metal gauzes, dip-coattechniques may be used.

The catalyst may comprise the catalytically active metal in any suitableamount to achieve the required level of activity. Typically, thecatalyst comprises the active metal in an amount in the range of from0.01 to 20% by weight, preferably from 0.02 to 10% by weight, morepreferably from 0.1 to 7.5% by weight.

The preferred reaction regime for use in the process is a fixed bedreaction regime, in which the catalyst is retained within a reactionzone in a fixed arrangement. If desired a fluidised bed, in which thecatalyst is employed in the form of particles fluidised by a stream ofgas can be used.

The fixed arrangement may be in the form of a fixed bed of catalystparticles, retained using fixed bed reaction techniques well known inthe art. Alternatively, the fixed arrangement may comprise the catalystin the form of a monolithic structure. A most preferred monolithicstructure comprises a ceramic foam. Suitable ceramic foams for use inthe process are available commercially. Alternative monolithicstructures include refractory oxide honeycomb monolith structures.Further, alternative forms of the fixed arrangement include arrangementsof metal gauzes or wires.

During the process, in accordance with the present invention, thefeedstock and the oxygen-containing gas are preferably contacted withthe catalyst under adiabatic conditions. For the purposes of thisspecification, the term “adiabatic” is a reference to reactionconditions in which substantially all heat loss and radiation from thereaction zone is prevented, with the exception of heat leaving in thegaseous effluent stream of the reactor.

Hydrogen or a mixture of hydrogen with other gases, prepared by theprocess of this invention may be particularly suitable for use as acombustible fuel, either directly or indirectly.

The process of this invention could very suitably be used to provide thehydrogen feed for a fuel cell. In fuel cells, hydrogen and oxygen arepassed over the fuel cell's catalyst in order to produce electricity andwater. Fuel cell technology is well known in the art. Fuel cells areknown to provide an environmentally-friendly source of energy.

It is preferred to enrich the synthesis gas in hydrogen and tosubstantially remove the carbon monoxide present, prior to usingsynthesis gas as a hydrogen source for fuel cells. Suitable methods toachieve this are known in the art. An example is the removal of carbonmonoxide, possibly together with other non-hydrogen synthesis gascomponents, by membrane separation. Another suitable method is pressureswing adsorption (PSA). It is particularly preferred to increase thehydrogen content of the synthesis gas by means of a water gas shiftreaction:

CO+H₂O→CO₂+H₂

The carbon dioxide thus-obtained may be removed by methods known in theart, for example membrane separation or PSA. The residual carbonmonoxide can suitably be removed by selective oxidation or, togetherwith the carbon dioxide, by membrane separation.

Accordingly, the present invention also relates to a process to generateelectrical energy comprising the following steps:

(a) the preparation of a mixture of hydrogen and carbon monoxide from anorganic feedstock according to the process of this invention; and

(b) the conversion of at least part of the hydrogen prepared in step (a)into electrical energy and water in a fuel cell.

Preferably, prior to the conversion of at least part of the hydrogen instep (b), the mixture of hydrogen and carbon monoxide prepared in step(a) is enriched in hydrogen by means of a water gas shift reaction,optionally followed by removal of carbon dioxide. More preferably, theresidual carbon monoxide is substantially removed from thehydrogen-enriched mixture of hydrogen and carbon monoxide by othermethods than a water gas shift reaction. Such methods are well known inthe art. Alternatively, the mixture of hydrogen and carbon monoxideprepared in step (a) is enriched in hydrogen by removal of carbonmonoxide by methods other than water gas shift reaction.

In a further aspect, the invention relates to an electrical-energygenerating system, wherein during operation electrical energy isgenerated by the electricity-generating process according to thisinvention.

Fuel cells are very suitable to apply in transport means, in particularautomotive vehicles or crafts. Accordingly, another aspect of thepresent invention relates to transport means provided with theelectrical-energy generating system of this invention.

EXAMPLE 1

a) Preparation of catalyst 0.1 g iridium (IV) chloride hydrate(IrCl₄.H₂O containing 53% wt of Ir ex Chempur) was dissolved in 1 gwater. The solution obtained was used to impregnate 1.0 g of YttriumPartial Stabilized Zirconia (Y-PSZ, commercially available having 650pores per square centimeter). The impregnation was carried out in threesteps with drying (at a temperature of about 100° C.) in between. Afterthe last impregnation, the material was calcined in air (1 hour at 700°C.) to decompose the iridium chloride.

b) catalytic experiment

Synthetic kerosene having a boiling range of from 150° C. to 200° C. andhaving a smoke point >50 mm was sprayed into an air stream using anozzle consisting of two concentric capillaries, the nozzle mouth wasmounted 2 centimeters away from the catalyst bed containing 0.87 g ofthe catalyst prepared according to part a) which catalyst was present ina quartz tube having an internal diameter of 12 mm. The catalyst bedvolume was 1.13 ml.

The experiment was carried out at a pressure of 3 bara. Kerosene was fedto the catalyst bed at a rate of 112,3 g/hour (154 ml/h) and air at arate of 470 Nl/hour. The GHSV (Gaseous Hourly Space Velocity) of the airamounted to 540,000 Nl/kg catalyst/hour. The experiment was carried outat a O₂/C ratio of 0.55.

Light-off of the experiment was achieved by co-feeding hydrogen andigniting by use of an infra-red lamp. The temperature of the top of thecatalyst bed stayed at about 1250° C.

The kerosene conversion amounted to 95%. The hourly yield amounted to4.8 10³ mol per kg of catalyst for carbon monoxide and to 3.7 10³ molper kg of catalyst for hydrogen. Under the operating conditions nocarbon build-up was visually observed.

EXAMPLE 2

a) Preparation of catalyst

11.5 g of a zirconium nitrate solution containing 14.6 wt % Zr was addedto 2.1 g iridium (IV) chloride hydrate (IrCl₄.H₂O containing 53% wt ofIr ex Chempur). The solution obtained was used to impregnate 20.00 g of30-80 mesh particles of Yttrium Partial Stabilized Zirconia (Y-PSZ,commercially available having 650 pores per square centimeter). Theimpregnation was carried out in four steps with drying (20 minutes at atemperature of about 140° C.) in between. After the last impregnation,the material was calcined in air (2 hour at 700° C.). The resultingcatalyst contained 4.7 wt % Ir and 7.1 wt % Zr based on the weight ofthe catalyst.

b) catalytic experiment

Synthetic kerosene having a boiling range of from 150° C. to 200° C. andhaving a smoke point >50 mm was sprayed into an air stream using anozzle consisting of two concentric capillaries, the nozzle mouth wasmounted 2 centimeters away from the catalyst bed containing 1.23 g ofthe catalyst prepared according to part a) which catalyst was present ina quartz tube having an internal diameter of 6 mm. The catalyst bedvolume was 0.6 ml.

The experiment was carried out at a pressure of 3 bara. Kerosene was fedto the catalyst bed at a rate of 158 g/hour (216 ml/h) and air at a rateof 600 Nl/hour. The GHSV (Gaseous Hourly Space Velocity) of the airamounted to 490,000 Nl/kg catalyst/hour. The experiment was carried outat a O₂/C ratio of 0.51.

Light-off of the experiment was achieved by co-feeding hydrogen andigniting by use of an infra-red lamp. The temperature of the top of thecatalyst bed stayed at about 1250° C.

The kerosene conversion amounted to 94%. The hourly yield amounted to5.6 10³ mol per kg of catalyst for carbon monoxide and to 5.4 10³ molper kg of catalyst for hydrogen. Under the operating conditions nocarbon build-up was visually observed.

What is claimed is:
 1. A catalytic partial oxidation process for thepreparation of hydrogen and carbon monoxide from an organic feedstock,which process comprises contacting the organic feedstock and anoxygen-containing gas, in amounts giving an oxygen-to-carbon ratio ofabout 0.3 to about 0.8, with a catalyst at a gas hourly space velocityof about 100,000 to about 10,000,000 Nl/kg/h, in which process theorganic feedstock used is a feedstock containing hydrocarbons and/oroxygenates, which feedstock is liquid under conditions of standardtemperature and pressure and has an average carbon number of at least 6.2. The process of claim 1, in which the feedstock has an average carbonnumber in the range of 6 to
 25. 3. The process of claim 1, in which thehydrocarbon feedstock has a boiling range of about 50° C. to about 500 °C.
 4. The process of claim 3, in which the feedstock comprises akerosene feedstock boiling between 150° C. and 200° C.
 5. The process ofclaim 3, in which the feedstock comprises a synthetic gasoil boilingbetween 200° C. and 500° C.
 6. The process of claim 1, in which thefeedstock comprises an alkanol or an ether.
 7. The process of claim 1,in which the feedstock and the oxygen-containing gas are present inamounts giving an oxygen-to-carbon ratio of 0.45 to 0.75.
 8. The processof claim 1, in which the feedstock is contacted with the catalyst at apressure of about 2 to about 50 bar.
 9. The process of claim 1, in whichthe feedstock is contacted with the catalyst at a temperature of about800 to about 1500° C.
 10. The process of claim 1, in which theoxygen-containing gas is contacted with the catalyst at a gas hourlyspace velocity of about 200,000 to about 3,000,000 Nl/kg/hr.
 11. Theprocess of claim 1, in which the catalyst comprises rhodium or iridium.12. The process of claim 1, in which the catalyst is retained in a fixedarrangement.
 13. The process of claim 1, in which the feedstock iscontacted with the catalyst under substantially adiabatic conditions.14. The process of claim 1, in which at least part of the feedstock ispresent in the form of visible droplets before entering into contactwith the catalyst.
 15. A process to generate electrical energycomprising the following steps: (a) preparing a mixture of hydrogen andcarbon monoxide from an organic feedstock using the process of claim 1;and (b) converting at least part of the hydrogen prepared in step (a)into electrical energy and water by means of a fuel cell.
 16. Theprocess of claim 15, wherein at least part of the mixture of hydrogenand carbon monoxide prepared in step (a) is enriched in hydrogen bymeans of a water gas shift reaction, optionally followed by removal ofcarbon dioxide.
 17. The process of claim 15, wherein at least part ofthe carbon monoxide is removed from the (hydrogen-enriched) mixture ofhydrogen and carbon monoxide by means other than a water gas shiftreaction.